Laser beam processing apparatus for processing semiconductor wafer in production of semiconductor devices, laser beam processing method executed therein, and such semiconductor wafer processed thereby

ABSTRACT

In a laser beam processing apparatus that processes a semiconductor wafer having a multi-layered wiring structure formed thereon, scribe lines defined thereon, and at least one alignment mark formed on any one of the scribe lines, a laser beam generator system generates a laser beam, and a movement system relatively moves the semiconductor wafer with respect to the laser beam such that the semiconductor wafer is irradiated with a laser beam along the scribe lines to partially remove the multi-layered wiring structure from the semiconductor wafer along the scribe lines. An irradiation control system controls the irradiation of the semiconductor wafer with the laser beam along the scribe lines such that the alignment mark is left on the scribe line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser beam processing apparatus thatprocesses a semiconductor wafer with a laser beam in production ofsemiconductor devices, and a laser beam processing method executed insuch a laser beam processing apparatus. Further, the present inventionrelates to a semiconductor wafer processed by the laser beam processingapparatus.

2. Description of the Related Art

In a representative process of producing a plurality of semiconductordevices, for example, a silicon wafer is prepared, and a surface of thesilicon wafer is sectioned into a plurality of semiconductor chip areaswhich are defined by grid-like scribe lines formed in the silicon wafer.Note, each of the scribe lines has a width falling within a rangebetween 40 μm and 70 μm.

The silicon wafer is processed by various well-known methods such thateach of the semiconductor chip areas is produced as a semiconductordevice, and a multi-layered wiring structure including a plurality ofwiring arrangement sections defined therein is formed over the siliconwafer such that the respective wiring arrangement sections are allocatedto the semiconductor devices, with the grid-like scribe lines beingcovered with multi-layered wiring structure.

Thereafter, the silicon wafer is subjected to a dicing process in whichthe plurality of semiconductor devices (i.e. bare chips) are cut alongthe grid-like scribe lines so as to be individually separated from eachother.

The dicing process is automatically carried out in a dicing apparatus.In particular, the dicing apparatus includes a table on which thesilicon wafer is mounted, and a rotary cutting blade which is associatedwith the table. During the dicing process, the rotary cutting blade isrotationally driven, and the table carrying the silicon wafer isautomatically moved with respect to the rotating cutting blade such thatthe silicon wafer is cut along the scribe lines. Before this automaticcutting operation can be properly carried out, the silicon wafer must beprecisely positioned at an initial position with respect to the rotatingcutting blade.

JP-A-H01-304721 discloses a silicon wafer which is provided with atleast one alignment mark formed on any one of cross points defined bythe grid-like scribe lines, and it is possible for the dicing apparatusto precisely position the silicon wafer at an initial position bydetecting the alignment mark. The alignment mark may be formed ofaluminum by using a photolithography process and an etching process.Note, in addition to the alignment mark, test electrode pads, testcircuit patterns and so on may be formed on the grid-like scribe lines,as disclosed in, for example, JP-2002-176140.

As well known, the multilayered wiring structure is composed ofinsulating interlayers and wiring metal pattern layers alternatelylaminated on each other, and each of the insulating interlayers is madeof suitable dielectric material, such as silicon dioxide, low-k materialor the like. These insulating interlayers are more fragile in comparisonwith the silicon wafer per se, and thus chips or cracks may easily occurin the multilayered wiring structure along the gridlike scribe linesthereof during the dicing process. When the chips or cracks penetrateinto one of the wiring arrangement sections allocated to thesemiconductor devices, the semiconductor device concerned becomesdefective. This problem has become more severe with the recent advanceof miniaturization of semiconductor devices, because the width of thegrid-like scribe lines has become narrower due to the advancedminiaturization.

It is proposed that the silicon wafer be processed by a laser beamprocessing apparatus before it is subjected to the dicing process, toprevent the penetration of the chips or cracks into the wiringarrangement sections allocated to the semiconductor devices, asdisclosed in, for example, JP-2002-329686 and JP-2003-320466. Inparticular, in the laser beam processing apparatus, the multi-layeredwiring structure is irradiated with a laser beam along the grid-likescribe lines so that only the multi-layered wiring structure is cut intothe wiring arrangement sections. In other words, the multi-layeredwiring structure is partially removed from the silicon wafer alonggrid-like scribe lines.

When the processed silicon wafer is transferred from the laser beamprocessing apparatus to a dicing apparatus, or when the processedsilicon wafer is shipped to a factory in which the processed siliconwafer is diced by using a dicing apparatus, it is difficult toefficiently and automatically carry out a dicing process in the dicingapparatus, because the alignment mark is eliminated from the processedsilicon wafer. In particular, as stated above, before an efficient andautomatic dicing process can be properly carried out, the silicon wafermust be precisely positioned at an initial position with respect to therotating cutting blade of the dicing apparatus. Nevertheless, it isimpossible to utilize the alignment mark for the precise positioning ofthe processed silicon wafer in the initial position.

SUMMARY OF THE INVENTION

Therefore, the present invention is directed to a laser beam processingapparatus that irradiates a multi-layered wiring structure on asemiconductor wafer with a laser beam along grid-like scribe lines so asto partially remove the multi-layered wiring structure along thegrid-like scribe lines in such a manner that at least one alignment markis left on the multi-layered wiring structure at a location on thegrid-like scribe lines.

The present invention is also directed to a laser beam processing methodexecuted in such a laser beam processing apparatus.

The present invention is further directed to a semiconductor waferprocessed by such a laser beam processing apparatus.

In accordance with a first aspect of the present invention, there isprovided a laser beam processing apparatus that processes asemiconductor wafer having a multi-layered wiring structure formedthereon, scribe lines defined thereon, and at least one alignment markformed on any one of the scribe lines, which comprises: a laser beamgenerator system that generates a laser beam; a movement system thatrelatively moves the semiconductor wafer with respect to the laser beamsuch that the semiconductor wafer is irradiated with a laser beam alongthe scribe lines to partially remove the multi-layered wiring structurefrom the semiconductor wafer along the scribe lines; and an irradiationcontrol system that controls the irradiation of the semiconductor waferwith the laser beam along the scribe lines such that the alignment markis left on the scribe line.

In this laser beam processing apparatus, the laser beam generator systemmay include a laser light source for producing the laser beam, and theirradiation control system includes a laser beam generator drivercircuit that drives the laser light source, a power of the laser beambeing decreased by controlling the laser beam generator driver circuitwhen the alignment mark is irradiated with the laser beam, whereby it isensured that the alignment mark is left on the scribe line.

Optionally, the laser beam generator system may include an opticaldeflector, and a driver circuit that drives the optical deflector, thelaser beam being deflected by controlling the driver circuit with theirradiation control system when an alignment mark area including thealignment mark is irradiated with the laser beam, whereby it is ensuredthat the alignment mark is left on the scribe line.

In accordance with a second aspect of the present invention, there isprovided a laser beam processing method comprising the steps of:preparing a semiconductor wafer having a multi-layered wiring structureformed thereon, scribe lines defined thereon, and at least one alignmentmark formed on any one of the scribe lines; generating a laser beam;relatively moving the semiconductor wafer with respect to the laser beamsuch that the semiconductor wafer is irradiated with a laser beam alongthe scribe lines to partially remove the multi-layered wiring structurefrom the semiconductor wafer along the scribe lines; and controlling theirradiation of the semiconductor wafer with the laser beam along thescribe lines such that the alignment mark is left on the scribe line.

In controlling the irradiation of the semiconductor wafer with the laserbeam along the scribe lines such that the alignment mark is left on thescribe line, a power of the laser beam may be decreased when thealignment mark is irradiated with the laser beam, whereby it is ensuredthat the alignment mark is left on the scribe line.

Optionally, the laser beam may be deflected when the alignment mark isirradiated with the laser beam, whereby it is ensured that the alignmentmark is left on the scribe line.

In accordance with a third aspect of the present invention, there isprovided a semiconductor wafer comprising: a substrate body; amulti-layered wiring structure formed on the substrate; scribe linesdefined on the multi-layered wiring structure; and at least onealignment mark formed on any one of the scribe lines, wherein themulti-layered wiring structure is partially removed from thesemiconductor wafer along the scribe lines, but the alignment mark isleft on the scribe line. A width of the scribe line may be within arange between 40 μm and 70 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other objects will be more clearly understood fromthe description set forth below, with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic perspective view showing an embodiment of a laserbeam processing apparatus according to the present invention;

FIG. 2 is a block diagram of a laser beam generator used in the laserbeam processing apparatus shown in FIG. 1;

FIG. 3 is a block diagram of the laser beam processing apparatus of FIG.1;

FIG. 4 is a plan view of a silicon wafer to be processed by the laserbeam processing apparatus according to the present invention, with thesilicon wafer being positioned at a first initial position;

FIG. 5A is a partially-enlarged plan view of the silicon wafer shown inFIG. 4;

FIG. 5B is a cross-sectional view taken along the 5B-5B line of FIG. 5A;

FIG. 6A is a partially-enlarged plan view, similar to FIG. 5A, of asilicon wafer, processed by the laser beam processing apparatusaccording to the present invention;

FIG. 6B is a cross-sectional view taken along the 6B-6B line of FIG. 6A;

FIG. 7 is a partial plan view of the silicon wafer for explainingdefinition of X-Y coordinates of the ends of each of scribe lines of thesilicon wafer;

FIG. 8 is a partial plan view of the silicon wafer for explainingdefinition of X-Y coordinates, derived from an X-Y coordinate of analignment marks, for leaving the alignment mark on the silicon wafer;

FIG. 9 is a plan view of the silicon wafer to be processed by the laserbeam processing apparatus according to the present invention, with thesilicon wafer being positioned at a second initial position;

FIG. 10 is a flowchart of a laser beam processing routine executed in asystem control unit shown in FIG. 3;

FIG. 11A is a part of a flowchart of a first laser beam irradiationroutine which is executed as a subroutine in the laser beam processingroutine of FIG. 10;

FIG. 11B is the remaining part of the flowchart of the first laser beamirradiation routine;

FIG. 12A is a part of a flowchart of a second laser beam irradiationroutine which is executed as a subroutine in the laser beam processingroutine of FIG. 10;

FIG. 12B is the remaining part of the flowchart of the second laser beamirradiation routine;

FIG. 13 is a partial plan view of a silicon wafer features scribe lineshaving a width of 70 μm, for explaining application of the presentinvention to such a silicon wafer;

FIG. 14 is a partial plan view, similar to FIG. 13, showing the siliconwafer featuring a set of longitudinal grooves G1 and G2 formed in amulti-layered wiring structure along a scribe line;

FIG. 15 is a schematic view of an acoustic optical modulator which maybe incorporated in a laser beam generator shown in FIG. 2; and

FIG. 16 is a partially-enlarged plan view, similar to FIG. 5A, showing asilicon wafer featuring an alignment mark which is out of a cross pointof scribe lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, an embodiment of a laser beam processingapparatus according to the present invention will be now explainedbelow.

The laser beam processing apparatus comprises a base frame 10, an X-Ymovable table machine, generally indicated by reference 12, mounted onthe base frame 10, and a laser beam processing machine, generallyindicated by reference 14, mounted on the base frame 10. Note, as shownin FIG. 1, an X-Y-Z coordinate system is defined with respect to thebase frame 10.

The X-Y movable table machine 12 includes a first pair of parallel guiderails 16 securely laid on the base frame 10 so as to be in parallel withan X-axis of the X-Y-Z coordinate system, and a first movable frame 18slidably mounted on the first parallel guide rails 16.

Although not visible in FIG. 1, the first movable frame 18 has a ballnut member provided on a bottom thereof, and the ball nut is engagedwith an elongated screw 20 provided between the parallel guide rails 16,and the elongated screw 20 is formed as an output shaft of a firststepping motor 22 securely provided on the base frame 10, with a freeend of the elongated screw 20 being rotatably supported by a first blockpiece 24 securely provided on the base frame 10. Thus, by driving thefirst stepping motor 22, it is possible to move the first movable frame18 along the parallel guide rails 16, and therefore, along the X-axis ofthe X-Y-Z coordinate system.

The X-Y movable table machine 12 also includes a second pair of parallelguide rails 26 securely laid on the first movable frame 18 so as to bein parallel with a Y-axis of the X-Y-Z coordinate system, and a secondmovable frame 28 slidably mounted on the parallel guide rails 26.

Although not visible in FIG. 1, the second movable frame 28 has a ballnut member provided on a bottom thereof, and the ball nut is engagedwith an elongated screw 30 provided between the parallel guide rails 26,and the elongated screw 30 is formed as an output shaft of a secondstepping motor 32 provided on the first movable frame 18, with a freeend of the elongated screw 30 being rotatably supported by a secondblock piece 34 securely provided on the first movable frame 18. Thus, bydriving the second stepping motor 32, it is possible to move the secondmovable frame 28 along the parallel guide rails 26, and therefore, alongthe Y-axis of the X-Y-Z coordinate system.

The X-Y movable table machine 12 further includes a cylindrical member36 securely provided on the second movable frame 28, a rectangular table38 securely provided on a top of the cylindrical member 36, and a chuckplate assembly 40 rotatably provided on the rectangular table 38. Thechuck plate assembly 40 can be rotated by driving a stepping motor 41(which is shown as a block in FIG. 3) contained in the cylindricalmember 36.

The chuck plate assembly 40 has a chuck plate 42 provided on a topthereof, and the chuck plate 42 has a plurality of holes formed therein.The chuck plate assembly 40 is constituted so as to allow it to becommunicated with a vacuum source (not shown). When a silicon wafer ismounted on the chuck plate 42, the communication is established betweenthe chuck plate assembly 40 and the vacuum source, and thus the siliconwafer is sucked to and immovably held on the chuck plate 42.

The laser beam processing machine 14 includes a pair of parallel guiderails 44 securely laid on the base frame 10 so as to be in parallel withthe Y-axis of the X-Y-Z coordinate system, and a movable frame 46slidably mounted on the parallel guide rails 44. The movable frame 46has a rectangular base portion 48 slidably engaged with the parallelguide rails 44, and an upright portion 50 integrally extended upwardfrom a side of the rectangular base portion 48. The upright portion 50is formed with a pair of guide rails 51 which are vertically extended inparallel with a Z-axis of the X-Y-Z coordinate system.

Although not visible in FIG. 1, the movable frame 46 has a ball nutmember provided on a bottom thereof, and the ball nut is engaged with anelongated screw 52 provided between the parallel guide rails 44, and theelongated screw 52 is formed as an output shaft of a stepping motor 54provided on the base frame 10, with a free end of the elongated screw 52being rotatably supported by a block piece (not visible) securelyprovided on the base frame 10. Thus, by driving the stepping motor 54,it is possible to move the movable frame 46 along the parallel guiderails 44, and therefore, the Y-axis of the X-Y-Z coordinate system.

The laser beam processing machine 14 also includes a block member 56slidably engaged with the guide rails 51 of the upright portion of themovable frame 46. The block member 56 has a ball nut member (notvisible) engaged with an elongated screw (not visible) provided betweenthe parallel guide rails 51, and the elongated screw is formed as anoutput shaft of a stepping motor 58 provided on a top of the uprightportion 50 of the movable frame 46. Thus, by driving the stepping motor58, it is possible to move the block member 56 along the parallel guiderails 51, and therefore, the Z-axis of the X-Y-Z coordinate system.

The laser beam processing machine 14 further includes a laser beamgenerator 60 supported by the block member 56 in a cantilever manner,and the laser beam generator 60 has a cylindrical casing 62, and a laserbeam irradiation head 64 attached to a free end of the cylindricalcasing 62.

As shown in FIG. 2, the laser beam generator 60 includes a laser lightsource 66, an optical modulator 68, and an optical focusing system 70contained in the cylindrical casing 62, and a beam bender 72 containedin the laser beam irradiation head 64. In this embodiment, the laserlight source 66 may be formed as a YAG laser light source. In FIG. 2, alaser beam LB is emitted from the laser light source 66, and then issuitably modulated by the optical modulator 68. The modulated laser beamis focused through the optical focusing system 70, and is reflected bythe beam bender 72 so as to be directed to the silicon wafer held on thechuck plate 42.

Further, the laser beam processing apparatus is provided with a CCD(charge-coupled device) camera 74 (which is shown as a block in FIG. 3).Although not shown in FIG. 1, the CCD camera 74 is immovably supportedby a suitable frame constructed on the base frame 10. Namely, the CCDcamera 74 is immovable with respect to the X-Y-Z coordinate system.

With reference to FIG. 3, the above-mentioned laser beam processingapparatus is illustrated as a block diagram of the laser beam processingapparatus.

As shown in this drawing, the laser beam processing apparatus includes asystem control unit 76 which contains a microcomputer having a centralprocessing unit (CPU), a read-only memory (ROM) for storing programs andconstants, a random-access memory (RAM) for storing temporary data, andan input/output (I/O) interface circuit.

The laser beam processing apparatus includes five driver circuits 78,80, 82, 84 and 86 for driving the respective stepping motors 22, 32, 41,54 and 58, and these stepping motors are controlled by the systemcontrol unit 76. Also, the laser beam processing apparatus includes alaser-beam generator driver circuit 88 for driving the laser beamgenerator 60, and a CCD driver circuit 90 for driving the CCD camera 74,and these driver circuits 88 and 90 are controlled by the system controlunit 76.

As shown in FIG. 3, the laser beam processing apparatus is provided witha keyboard 92 for inputting various commands and data to the systemcontrol unit 76 through the I/O interface circuit thereof, a TV monitor94 for displaying various command items, various information data and soon, and a mouse 96 for inputting a command to the system control unit 76by clicking the mouse 96 on any one of the command items displayed onthe TV monitor 94.

The laser beam processing apparatus further includes a hard disk driver98 for driving a hard disk 100, on which various data are stored. Thesystem control unit 76 writes the various data in the hard disk 100through the hard disk driver 98, and also reads the various data fromthe hard disk 100 through the hard disk driver 98.

FIG. 4 shows a silicon wafer SW which should be processed by theabove-mentioned laser beam processing apparatus, FIG. 5A shows a part ofthe silicon wafer SW in an enlarged view, and FIG. 5B shows a crosssection of the silicon wafer SW taken along the 5B-5B lines of FIG. 5A.As shown in FIG. 4, the silicon wafer SW is provided with an orientationflat, indicated by reference OF, which is used to orient and positionthe silicon wafer SW in various processings.

As shown in FIGS. 4 and 5A, a surface of the silicon wafer SW issectioned into a plurality of semiconductor chip areas CA which aredefined by a first group of scribe lines FSL_(m) and a second group ofscribe lines SSL_(n), the scribe lines FSL_(m) and scribe lines SSL_(n)being intersected with each other so as to define a grid. Note, in thisembodiment, the number of the scribe lines FSL_(m) is twenty three (m=1,2, . . . 22 and 23), and the number of the scribe lines SSL_(n) istwenty two (n=1, 2, . . . 21 and 22). The first group of scribe linesFSL_(m) is perpendicular to the orientation flat OF, and the secondgroup of scribe lines SSL_(n) is in parallel to the orientation flat OF.In this embodiment, the pitch of the scribe lines FSL_(m) issubstantially the same as that of the scribe lines SSL_(n), and each ofthe scribe lines FSL_(m) and SSL_(n) has a width of 40 μm.

The silicon wafer SW is processed by various well-known methods suchthat each of the semiconductor chip areas CA is produced as asemiconductor device, and a multi-layered wiring structure MWS includinga plurality of wiring arrangement sections defined therein is formedover the silicon wafer SW, as illustrated in FIG. 5B, with therespective wiring arrangement sections being allocated to thesemiconductor devices or semiconductor chip areas CA.

As shown in FIGS. 5A and 5B, electrode pads EP are formed on a surfaceof the multi-layered wiring structure MWS at each of the semiconductorchip areas CA, and test electrode pads TEP are formed on the surface ofthe multi-layered wiring structure MWS along each of the scribe linesFSL_(m) and SSL_(n).

In this embodiment, the silicon wafer SW has two diamond-shapedalignment marks AM formed thereon, and only one of the alignment marksAM is illustrated in FIGS. 5A and 5B. The respective alignment marks AMare positioned at locations indicated by references L1 and L2 in FIG. 4.The location L1 is defined as a cross point of the scribe lines FSL₅ andSSL₁₉, and the location L2 is defined as a cross point of the scribelines FSL₁₉ and SSL₃. Note, in this embodiment, the locations L1 and L2are symmetrical with respect to a center of the silicon wafer SWindicated by reference C in FIG. 4.

According to the present invention, the silicon wafer SW is processed bythe above-mentioned laser beam processing apparatus, so that only themulti-layered wiring structure MWS of the silicon wafer SW is cut intothe wiring arrangement sections by irradiating the multi-layered wiringstructure MWS with a laser beam along the scribe lines FSL_(m) andSSL_(n) in such a manner that alignment mark areas AMA including therespective alignment marks AM are left on the multi-layer wiringstructure MWS, as representatively shown in FIGS. 6A and 6B. In otherwords, the multi-layered wiring structure MWS is partially removed fromthe silicon wafer SW along the scribe lines FSL_(m) and SSL_(n) in sucha manner that grid-like grooves G are formed in the multi-layered wiringstructure MWS except for the alignment mark areas AMA. Note, in thisembodiment, the laser beam has a spot diameter of 20 μm.

In particular, in this embodiment, first, the silicon wafer SW issecurely mounted on the chuck plate 42, and is then positioned bysuitably driving the stepping motors 22 and 32 to a first initialposition at which the orientation flat OF of the silicon wafer SW is inparallel to the X-axis of the X-Y-Z coordinate system (FIG. 1), as shownin FIG. 4. Thereafter, by suitably driving the stepping motors 22 and32, the first group of scribe lines FSL_(m) are irradiated in order withthe laser beam emitted from the laser beam irradiation head 64,resulting in the partial removal of the multi-layered wiring structureMWS from the silicon wafer SW along the scribe lines FSL_(m).

In order to carry out the partial removal of the multi-layered wiringstructure MWS from the silicon wafer SW along the scribe lines FSL_(m)in the laser beam processing apparatus shown in FIG. 1, X-Y coordinatedata FE1 _(m)(fx1 _(m); fy1 _(m)) and FE2 _(m)(fx2 _(m); fy2 _(m)),which represent the ends of each of the scribe lines FSL_(m) when thesilicon wafer SW is positioned at the first initial position, arepreviously prepared and stored on the hard disk 100. As representativelyshown in FIG. 7, each of the X-Y coordinates FE1 _(m)(fx1 _(m); fy1_(m)) and FE2 _(m)(fx2 _(m); fy2 _(m)) is defined as a point sited on alongitudinal central axis LSA of a scribe line FSL_(m) at the endsthereof.

Also, in order to leave the alignment mark areas AMA at the locations L1and L2 (FIG. 4), X-Y coordinate data FAL1 _((−FL1))(fx1 ₅; fy1_((−FL1))) and FAL1 _((+FL1))(fx1 ₅; fy1 _((+FL1))) and X-Y coordinatedata FAL2 _((−FL2))(fx1 ₁₉; fy1 _((−FL2))) and FAL2 _((+FL2))(fx1 ₁₉;fy1 _((+FL2))), which are derived from respective X-Y coordinates of thealignment marks AM positioned in the locations L1 and L2, are previouslyprepared and stored on the hard disk 100.

For example, as shown in FIG. 8, when the X-Y coordinate of thealignment mark AM positioned in the location L1 is represented byFAM1(fx_(L1); fy_(L1)), the Y-coordinates fy1 _((−FL1)) and fy1_((+FL1)) of the X-Y coordinate data FAL1 _((−FL1)) and FAL1 _((+FL1))are defined as follows:fy1_((−FL1)) =fy _(L1)−½W _(G)−αfy1_((+FL1)) fy _(L1)+½W _(G)+αHerein: α is a distance corresponding to a half of the spot diameter (20μm) of the laser beam, and W_(G) is a width of the grid-like grooves G.

Similarly, when the X-Y coordinate of the alignment mark AM positionedin the location L2 is represented by FAM2(fx_(L2); fy_(L2)), theY-coordinates fy1 _((−FL2))and fy1 _((+FL2)) of the X-Y coordinate dataFAL2 _((−FL2)) and FAL2 _((+FL2)) are defined as follows:fy1_((−FL2)) =fy _(L2)−½W _(G)−αfy1_((+FL2)) =fy _(L2)+½W _(G)+α

After the partial removal of the multi-layered wiring structure MWS fromthe silicon wafer SW along the scribe lines FSL_(m), the stepping motor41 contained in the cylindrical member 36 is driven so that the siliconwafer SW is rotated clockwise by an angle of 90 degrees, as shown inFIG. 9. Then, the silicon wafer SW is positioned by suitably driving thestepping motors 22 and 32 to a second initial position at which theorientation flat OF of the silicon wafer SW is in parallel to the Y-axisof the X-Y-Z coordinate system (FIG. 1) . Thereafter, by suitablydriving the stepping motors 22 and 32, the second group of scribe linesSSL_(n) are irradiated in order with the laser beam emitted from thelaser beam irradiation head 64, resulting in the partial removal of themulti-layered wiring structure MWS from the silicon wafer SW along thescribe lines SSL_(n).

In order to carry out the partial removal of the multi-layered wiringstructure MWS from the silicon wafer SW along the scribe lines SSL_(n)in the laser beam processing apparatus shown in FIG. 1, X-Y coordinatedata SE1 _(n)(sx1 _(n); sy1 _(n)) and SE2 _(n)(sx2 _(n); sy2 _(n)),which represent the ends of each of the scribe lines SSL_(n) when thesilicon wafer SW is positioned at the second initial position, arepreviously prepared and stored on the hard disk 100.

Also, in order to leave the alignment mark areas AMA at the locations L1and L2 (FIG. 9), X-Y coordinate data SAL1 _((−SL1))(sx1 ₅; sy1_((−SL1))) and SAL1 _((+SL1))(sx1 ₅; sy1 _((+SL1))) and X-Y coordinatedata SAL2 _((−SL2))(sx1 ₁₉; sy1 _((−SL2))) and SAL2 _((+SL2))(sx1 ₁₉;sy1 _((+SL2))), which are derived from respective X-Y coordinates of thealignment marks AM positioned in the locations L1 and L2, are previouslyprepared and stored on the hard disk 100.

Similar to the aforesaid X-Y coordinate data FAL_((−FL1)) (fx1 ₅; fy1_((−FL1))) and FAL1 _((+FL1)) (fx1 ₅; fy1 _((+FL1))) and X-Y coordinatedata FAL2 _((−FL2)) (fx1 ₁₉; fy1 _((−FL2))) and FAL2 _((+FL2)) (fx1 ₁₉;fy1 _((+FL2))), when the respective X-Y coordinates of the alignmentmarks AM positioned in the locations Ll and L2 is represented by SAM1(sx_(L1); sy_(L1)) and SAM2(sx_(L2); sy_(L2)), the Y-coordinates sy1_((−SL1)) and sy1 _((+SL1)) of the X-Y coordinate data SAL1 _((SL1)) andSAL1 _((+SL1)) and the Y-coordinates sy2 _((−SL2)) and sy2 _((+SL2)) ofthe X-Y coordinate data SAL2 _((−SL2)) and SAL2 _((+SL2)) are defined asfollows:sy1_((−SL1)) =sy _(L1)−½W _(G)−αsy1_((+SL1)) =sy _(L1)+½W _(G)+αsy1_((−SL2)) =sy _(L2)+½W _(G)−αsy1_((+SL2)) =sy _(L2)+½W _(G)+α

According to the present invention, when the processed silicon wafer SWis diced by using a dicing apparatus, it is possible to efficiently andautomatically carry out a dicing process in the dicing apparatus,because the processed silicon wafer SW can be precisely positioned at aninitial position with respect to the rotating cutting blade of thedicing apparatus by using the alignment marks AM left on the processedsilicon wafer SW.

FIG. 10 shows a flowchart of a laser beam processing routine which isexecuted in the system control unit 76 shown in FIG. 3. Note, forexample, an execution of the laser beam processing routine is started byclicking the mouse 96 on a routine-starting icon on the screen of the TVmonitor 94, and an initial scene is displayed on the screen of the TVmonitor 94. Also note, prior to the execution of the laser beamprocessing routine, the silicon wafer SW, as shown in FIGS. 4, 5A and5B, is securely sucked and held on the chuck plate 42.

At step 1001, it is monitored whether various data are input to thesystem control unit 76 through a manipulation of the keyboard 92.Alternatively, these data may be input to the system control unit 76 byclicking the mouse 96 on data items displayed on the screen of the TVmonitor 94.

Among the various data, there are size data SD of the silicon wafer SWto be processed, pitch data PD of the scribe lines FSL_(m) and SSL_(n),and width data WD of the grid-like scribe lines FSL_(m) and SSL_(n).Also, among the various data, there are scribe line data FSL₅ andSSL_(n) and scribe line data FSL₁₉ and SSL₃ which are associated withthe respective alignment marks AM.

When the inputting of the various data is confirmed, the controlproceeds to step 1002, in which a first irradiation head positioningroutine is executed based on the size data SD, pitch data PD and widthdata WD. Namely, the stepping motor 54 is driven by the driver circuit84 such that the laser beam irradiation head 64 is positioned at a firstlaser beam irradiation starting position which is previously determinedwith respect to the silicon wafer SW featuring the size data SD, pitchdata PD and width data WD.

After the execution of the first irradiation head positioning routine,the control proceeds to step 1003, in which an alignment mark detectionroutine is executed. Namely, image data of the silicon wafer SW arefetched from the CCD camera 74 through the CCD driver circuit 90, andare processed in the control system unit 76 so as to detect image dataof the alignment marks AM therefrom. Then, X-Y coordinates of thealignment marks AM are determined with respect to the X-Y-Z coordinatesystem (FIG. 1) based on the detected image data of the alignment marksAM.

After the execution of the alignment mark detection routine, the controlproceeds to step 1004, in which a first initial-positioning routine forpositioning the silicon wafer SW at the aforesaid first initial positionbased on the X-Y coordinates of the detected alignment marks AM isexecuted. In particular, the respective stepping motors 22 and 32 aredriven by the driver circuits 78 and 80 under control of the systemcontrol unit 76, based on the X-Y coordinates of the detected alignmentmarks AM, resulting in the positioning of the silicon wafer SW at thefirst initial position.

Note, when the silicon wafer SW is positioned at the first initialposition, the laser beam irradiation head 64 is placed just above theX-Y coordinates FE1 ₁(fx1 ₁; fy1 ₁). Thus, when a laser beam is emittedfrom the laser beam irradiation head 64, a location on the silicon waferSW, represented by the X-Y coordinates FE1 ₁(fx1 ₁; fy1 ₁), isirradiated with the emitted laser beam.

After the execution of the first initial-positioning routine, thecontrol proceeds to step 1005, in which a first laser beam irradiationroutine is executed. In the execution of the first laser beamirradiation routine, the multi-layered wiring structure MWS is partiallyremoved from the silicon wafer SW along the scribe lines FSL_(m) in sucha manner that the grid-like grooves G are formed in the multi-layeredwiring structure MWS along the scribe lines FSL_(m) except for thealignment mark areas AMA. Note, the first laser beam irradiation routineis explained in detail hereinafter, with reference to FIGS. 11A and 11B.

After the execution of the first laser beam irradiation routine, thecontrol proceeds to step 1006, in which the stepping motor 41 containedin the cylindrical member 36 is driven so that the silicon wafer SW isrotated by an angle of 90 degrees (FIG. 9).

Then, at step 1007, a second irradiation head positioning routine isexecuted based on the size data SD, pitch data PD and width data WD.Namely, the stepping motor 54 is driven by the driver circuit 84 suchthat the laser beam irradiation head 64 is positioned at a second laserbeam irradiation starting position which is previously determined withrespect to the 90-degree rotated silicon wafer SW featuring the sizedata SD, pitch data PD and width data WD.

After the execution of the second irradiation head positioning routine,the control proceeds to step 1008, in which a second initial-positioningroutine for positioning the 90-degree rotated silicon wafer SW at theaforesaid second initial position is executed. In particular, therespective stepping motors 22 and 32 are driven by the driver circuits78 and 80 under control of the system control unit 76, resulting in thepositioning of the silicon wafer SW at the second initial position.

Note, when the silicon wafer SW is positioned at the second initialposition, the laser beam irradiation head 64 is placed just above theX-Y coordinates SE1 ₁(sx1 ₁; sy1 ₁). Thus, when a laser beam is emittedfrom the laser beam irradiation head 64, a location on the silicon waferSW, represented by the X-Y coordinates SE1 ₁(sx1 ₁; sy1 ₁), isirradiated with the emitted laser beam.

After the execution of the second initial-positioning routine, thecontrol proceeds to step 1009, in which a second laser beam irradiationroutine is executed. In the execution of the second laser beamirradiation routine, the multi-layered wiring structure MWS is partiallyremoved from the silicon wafer SW along the scribe lines SSL_(n) in sucha manner that the grid-like grooves G are formed in the multi-layeredwiring structure MWS along the scribe lines SSL_(n) except for thealignment mark areas AMA. Note, the second laser beam irradiationroutine is explained in detail hereinafter, with reference to FIGS. 12Aand 12B.

After the execution of the second laser beam irradiation routine, thecontrol proceeds to step 1010, in which it is determined whether thelaser beam processing routine should be repeated, i.e. whether a siliconwafer SW remains to be processed. When the existence of a remainingsilicon wafer SW is confirmed, the control returns to step 1002. Whenthere is no silicon wafer to be tested, the routine ends.

FIGS. 11A and 11B show a flowchart of the first laser beam irradiationroutine which is executed as a subroutine in step 1005 of FIG. 10. Note,in reality, although the silicon wafer SW is moved with respect to thelaser beam irradiation head 64 to irradiate the scribe lines FSL_(m)with the laser beam, it is presumed that the laser beam irradiation head64, and therefore, the laser beam, is moved with respect to the siliconwafer SW for the sake of explanatory convenience.

At step 1101, a counter m is initialized to be “1”. Then, at step 1102,the X-Y coordinate data FE1 _(m)(fx1 _(m); fy1 _(m)) and FE2 _(m)(fx2_(m); fy2 _(m)), the coordinate data FAL1 _((−FL1))(fx1 ₅; fy1_((−FL1))) and FAL1 _((+FL1))(fx1 ₅; fy1 _((+FL1))) and the coordinatedata FAL2 _((−FL2))(fx1 ₁₉; fy1 _((−FL2))) and FAL2 _((+FL2))(fx1 ₁₉;fy1 _((+FL2))) are read from the hard disk 100, and are then stored inthe random-access memory (RAM) contained in the system control unit 76.

At step 1103, the laser light source 66 of the laser beam generator 60is energized by the laser beam generator driver circuit 88 under controlof the system control unit 76, so that the laser beam is emitted fromthe laser beam irradiation head 64, whereby the location on the siliconwafer SW, represented by the X-Y coordinates FE1 ₁(fx1 ₁; fy1 ₁), isirradiated with the emitted laser beam. Of course, the laser beam has asufficient power to remove the materials of the multi-layered wiringstructure MWS.

At step 1104, the laser beam irradiation head 64, and therefore, thelaser beam, is moved with respect to the silicon wafer SW along theY-axis of the X-Y-Z coordinate system in a direction indicated byreference Yl in FIG. 4, i.e., in reality, the stepping motor 32 isdriven so that the silicon wafer SW is moved along the Y-axis of theX-Y-Z coordinate system in a direction indicated by reference Y2 in FIG.4.

At step 1105, it is determined whether a count number of the counter mhas reached “5”. When the count number of the counter m has not reached“5”, the control proceeds from to step 1105 to step 1106, in which it isdetermined whether the count number of the counter m has reached “19”.When the count number of the counter m has not reached “19”, the controlproceeds from step 1106 to step 1107, in which it is monitored whetherthe laser beam has arrived at the Y-coordinate fy2 _(m). When it isconfirmed that the laser beam has arrived at the Y-coordinate fy2 _(m),the control proceeds to step 1108, in which the power of the laser beamis decreased by controlling the laser beam generator driver circuit 88so that none of the materials of the multi-layered wiring structure MWSare removed. Note, at step 1108, the energization of the laser lightsource 66 may be stopped, if necessary.

At step 1109, the count number of the counter m is incremented by “1”.Then, at step 1110, it is determined whether the count number of thecounter m is smaller than “23”. If m<23, the control proceeds to step1111, in which it is monitored whether the laser beam has arrived at theY-coordinate fy2 _(m). When it is confirmed that the laser beam hasarrived at the Y-coordinate fy2 _(m), the control proceeds to step 1112,in which the movement of the laser beam is stopped.

At step 1113, the laser beam is moved with respect to the silicon waferSW along the X-axis of the X-Y-Z coordinate system in a directionindicated by reference X1 in FIG. 4, i.e., in reality, the steppingmotor 22 is driven so that the silicon wafer SW is moved along theX-axis of the X-Y-Z coordinate system in a direction indicated byreference X2 in FIG. 4.

At step 1114, it is monitored whether the laser beam has arrived the X-Ycoordinate FE2 _(m)(fx2 _(m); fy2 _(m)). When it is confirmed that thelaser beam has arrived at X-Y coordinate FE2 _(m)(fx2 _(m); fy2 _(m)),the control proceeds to step 1115, in which the movement of the laserbeam is stopped. Then, at step 1116, the power of the laser beam isincreased, and, at step 1117, the laser beam is moved with respect tothe silicon wafer SW along the Y-axis of the X-Y-Z coordinate system inthe direction indicated by reference Y2 in FIG. 4, i.e., in reality, thestepping motor 32 is driven so that the silicon wafer SW is moved alongthe Y-axis of the X-Y-Z coordinate system in the direction Y1 (FIG. 4).

At step 1118, it is monitored whether the laser beam has arrived at theY-coordinate fy1 _(m). When it is confirmed that the laser beam hasarrived at the Y-coordinate fy1 _(m), the control proceeds to step 1119,in which the power of the laser beam is decreased by controlling thelaser beam generator driver circuit 88, so that none of the materials ofthe multi-layered wiring structure MWS are removed.

At step 1120, the count number of the counter m is incremented by “1”.Then, at step 1121, it is monitored whether the laser beam has arrivedat the Y-coordinate fy1 _(m). When it is confirmed that the laser beamhas arrived at the Y-coordinate fy1 _(m), the control proceeds to step1122, in which the movement of the laser beam is stopped.

At step 1123, the laser beam is moved with respect to the silicon waferSW along the X-axis of the X-Y-Z coordinate system in the direction X1(FIG. 4), i.e., in reality, the stepping motor 22 is driven so that thesilicon wafer SW is moved along the X-axis of the X-Y-Z coordinatesystem in the direction X2.

At step 1124, it is monitored whether the laser beam has arrived the X-Ycoordinate FE1 _(m)(fx1 _(m); fy1 _(m)). When it is confirmed that thelaser beam has arrived at the X-Y coordinate FE1 _(m)(fx1 _(m); fy1_(m)), the control proceeds to step 1125, in which the movement of thelaser beam is stopped. Then, at step 1126, the power of the laser beamis increased, and the control returns to step 1104.

At step 1105, when the count number of the counter m has reached “5”,the control proceeds to step 1127, in which it is monitored whether thelaser beam has arrived at the Y-coordinate fy1 _((−FL1)) (FIG. 8). Whenit is confirmed that the laser beam has arrived at the Y-coordinate fy1_((−FL1)), the control proceeds to step 1128, in which the power of thelaser beam is decreased by controlling the laser beam generator drivercircuit 88, so that the alignment mark AM positioned at the location L1cannot be removed.

At step 1129, it is monitored whether the laser beam has arrived at theY-coordinate fy1 _((+FL1)) (FIG. 8). When it is confirmed that the laserbeam has arrived at the Y-coordinate fy1 _((+FL1)), the control proceedsto step 1130, in which the power of the laser beam is increased. Then,the control returns to step 1107.

At step 1106, when the count number of the counter m has reached “19”,the control proceeds to step 1131, in which it is monitored whether thelaser beam has arrived at the Y-coordinate fy1 _((−FL2)). When it isconfirmed that the laser beam has arrived at the Y-coordinate fy1_((−FL2)), the control proceeds to step 1132, in which the power of thelaser beam is decreased by controlling the laser beam generator drivercircuit 88, so that the alignment mark AM positioned at the location L2cannot be removed.

At step 1133, it is monitored whether the laser beam has arrived at theY-coordinate fy1 _((+FL2)). When it is confirmed that the laser beam hasarrived at the Y-coordinate fy1 _((+FL2)), the control proceeds to step1134, in which the power of the laser beam is increased. Then, thecontrol returns to step 1107.

At step 1110, when the count number of the counter m has reached “23”,the control returns to step 1005 of the laser beam processing routine ofFIG. 10.

FIGS. 12A and 12B show a flowchart of the second laser beam irradiationroutine which is executed as a subroutine in step 1009 of FIG. 10.Similar to the first laser beam irradiation routine of FIGS. 11A and11B, in reality, although the silicon wafer SW is moved with respect tothe laser beam irradiation head 64 to irradiate the scribe lines SSL_(n)with the laser beam, it is presumed that the laser beam irradiation head64, and therefore, the laser beam, is moved with respect to the siliconwafer SW for the sake of explanatory convenience.

At step 1201, a counter n is initialized to be “1” . Then, at step 1202,the X-Y coordinate data SE1 _(n)(sx1 _(n); sy1 _(n)) and SE2 _(n)(sx2_(n); sy2 _(n)), the coordinate data SAL1 _((−SL1))(sx1 ₁₉; sy1_((−SL1))) and SAL1 _((+SL1))(sx1 ₁₉; sy1 _((+SL1))) and the coordinatedata SAL2 _((−SL2))(sx1 ₃; sy1 _((−SL2))) and SAL2 _((+SL2))(sx1 ₃; sy1_((+SL2))) are read from the hard disk 100, and are then stored in therandom-access memory (RAM) contained in the system control unit 76.

At step 1203, the laser light source 66 of the laser beam generator 60is energized by the laser beam generator driver circuit 88 under controlof the system control unit 76, so that the laser beam is emitted fromthe laser beam irradiation head 64, whereby the location on the siliconwafer SW, represented by the X-Y coordinates SE1 ₁(sx1 ₁; sy1 ₁), isirradiated with the emitted laser beam. Of course, the laser beam has asufficient power to remove the materials of the multi-layered wiringstructure MWS.

At step 1204, the laser beam irradiation head 64, and therefore, thelaser beam, is moved with respect to the silicon wafer SW along theY-axis of the X-Y-Z coordinate system in the direction Y1 (FIG. 4),i.e., in reality, the stepping motor 32 is driven so that the siliconwafer SW is moved along the Y-axis of the X-Y-Z coordinate system in thedirection Y2.

At step 1205, it is determined whether a count number of the counter nhas reached “3”. When the count number of the counter n has not reached“3”, the control proceeds from step 1205 to step 1206, in which it isdetermined whether the count number of the counter n has reached “19”.When the count number of the counter n has not reached “19”, the controlproceeds from step 1206 to step 1207, in which it is monitored whetherthe laser beam has arrived at the Y-coordinate sy2 _(n). When it isconfirmed that the laser beam has arrived at the Y-coordinate sy2 _(n),the control proceeds to step 1208, in which the power of the laser beamis decreased by controlling the laser beam generator driver circuit 88so that none of the materials of the multi-layered wiring structure MWSare removed. Note, at step 1208, the energization of the laser lightsource 66 may be stopped, if necessary.

At step 1209, the count number of the counter n is incremented by “1”.Then, at step 1210, it is determined whether the count number of thecounter n is smaller than “22”. If n<22, the control proceeds to step1211, in which it is monitored whether the laser beam has arrived at theY-coordinate sy2 _(n). When it is confirmed that the laser beam hasarrived at the Y-coordinate sy2 _(n), the control proceeds to step 1212,in which the movement of the laser beam is stopped.

At step 1213, the laser beam is moved with respect to the silicon waferSW along the X-axis of the X-Y-Z coordinate system in the direction X1(FIG. 9), i.e., in reality, the stepping motor 22 is driven so that thesilicon wafer SW is moved along the X-axis of the X-Y-Z coordinatesystem in the direction X2.

At step 1214, it is monitored whether the laser beam has arrived the X-Ycoordinate SE2 _(n)(sx2 _(n); sy2 _(n)). When it is confirmed that thelaser beam has arrived at X-Y coordinate SE2 _(n)(sx2 _(n); sy2 _(n)),the control proceeds to step 1215, in which the movement of the laserbeam is stopped. Then, at step 1216, the power of the laser beam isincreased, and, at step 1217, the laser beam is moved with respect tothe silicon wafer SW along the Y-axis of the X-Y-Z coordinate system inthe direction Y2 (FIG. 9), i.e., in reality, the stepping motor 32 isdriven so that the silicon wafer SW is moved along the Y-axis of theX-Y-Z coordinate system in the direction Y1.

At step 1218, it is monitored whether the laser beam has arrived at theY-coordinate sy1 _(n). When it is confirmed that the laser beam hasarrived at the Y-coordinate sy1 _(n), the control proceeds to step 1219,in which the power of the laser beam is decreased by controlling thelaser beam generator driver circuit 88, so that none of the materials ofthe multi-layered wiring structure MWS are removed.

At step 1220, the count number of the counter n is incremented by “1”.Then, at step 1221, it is monitored whether the laser beam has arrivedat the Y-coordinate sy1 _(n). When it is confirmed that the laser beamhas arrived at the Y-coordinate sy1 _(n), the control proceeds to step1222, in which the movement of the laser beam is stopped.

At step 1223, the laser beam is moved with respect to the silicon waferSW along the X-axis of the X-Y-Z coordinate system in the direction X1(FIG. 9), i.e., in reality, the stepping motor 22 is driven so that thesilicon wafer SW is moved along the X-axis of the X-Y-Z coordinatesystem in the direction indicated by reference X2.

At step 1224, it is monitored whether the laser beam has arrived the X-Ycoordinate SE1 _(n)(sx1 _(n); sy1 _(n)) . When it is confirmed that thelaser beam has arrived at the X-Y coordinate SE1 _(n)(sx1 _(n); sy1_(n)), the control proceeds to step 1225, in which the movement of thelaser beam is stopped. Then, at step 1226, the power of the laser beamis increased, and the control returns to step 1204.

At step 1205, when the count number of the counter n has reached “3”,the control proceeds to step 1227, in which it is monitored whether thelaser beam has arrived at the Y-coordinate sy1 _((−SL2))). When it isconfirmed that the laser beam has arrived at the Y-coordinate sy1_((−SL2)), the control proceeds to step 1228, in which the power of thelaser beam is decreased by controlling the laser beam generator drivercircuit 88, so that the alignment mark AM positioned at the location L2cannot be removed.

At step 1229, it is monitored whether the laser beam has arrived at theY-coordinate sy1 _((+SL2)). When it is confirmed that the laser beam hasarrived at the Y-coordinate sy1 _((+SLZ)), the control proceeds to step1230, in which the power of the laser beam is increased. Then, thecontrol returns to step 1207.

At step 1206, when the count number of the counter n has reached “19”,the control proceeds to step 1231, in which it is monitored whether thelaser beam has arrived at the Y-coordinate sy1 _((−SL1)). When it isconfirmed that the laser beam has arrived at the Y-coordinate sy1_((−SL1)), the control proceeds to step 1232, in which the power of thelaser beam is decreased by controlling the laser beam generator drivercircuit 88, so that the alignment mark AM positioned at the location L1cannot be removed.

At step 1233, it is monitored whether the laser beam has arrived at theY-coordinate sy1 _((+SL1)). When it is confirmed that the laser beam hasarrived at the Y-coordinate sy1 _((+SL1)), the control proceeds to step1234, in which the power of the laser beam is increased. Then, thecontrol returns to step 1207.

At step 1210, when the count number of the counter n has reached “22”,the control returns to step 1009 of the laser beam processing routine ofFIG. 10.

With reference to FIG. 13, a part of a silicon wafer SW is illustratedin a plan view. This silicon wafer SW features scribe lines FSL_(m) andSSL_(n) having a width of 70 μm. In this case, it is not easy toeffectively remove the multi-layered wiring structure from the siliconwafer SW along scribe lines FSL_(m) and SSL_(n) by irradiating it with alaser beam, because a spot diameter of the laser beam is usually withina range from 10 μm to 20 μm.

According to the present invention, the scribe lines FSL_(m) andSSL_(n), are defined along the sides of each of the scribe lines FSL_(m)and SSL_(n), and each of the scribe lines FSL_(m) and SSL_(n) isirradiated with the laser beam along the longitudinal side axes LSA1 andLSA2, using the laser beam processing apparatus as shown in FIG. 1, sothat a set of longitudinal grooves G1 and G2 are formed in themulti-layered wiring structure, as shown in FIG. 14. Namely, a materialof the multi-layered wiring structure is left on each of the scribelines FSL_(m) and SSL_(n) along a longitudinal center thereof.

During a dicing process of this silicon wafer SW, although chips orcracks may occur in the material of the multi-layered wiring structureleft on each of the scribe lines FSL_(m) and SSL_(n), the chips orcracks cannot penetrate into the wiring arrangement sections allocatedto the respective semiconductor chip areas CA, due to the existence ofthe grooves G1 and G2.

By suitably defining a set of X-Y coordinates at the ends of each of thescribe lines FSL_(m) and SSL_(n) on each of the longitudinal side axesLSA1 and LSA2, it is possible to automatically carry out the irradiationof the scribe lines FSL_(m) and SSL_(n) with the laser beam, using thelaser beam processing apparatus according to the present invention. Ofcourse, the irradiation of the scribe lines FSL_(m) and SSL_(n) with thelaser is performed such that an alignment mark is left on one of thescribe lines FSLM and SSL_(n), in substantially the same manner asmentioned above.

In the aforesaid embodiment, when the irradiation of a scribe line(FSL_(m), SSL_(n)) with the laser beam is completed, or when thealignment mark areas AMA is defined, the power of the laser beam isdecreased by controlling the laser beam generator driver circuit 88.Namely, the power of the laser beam is frequently varied, and thus thepower of the laser beam is liable to be unstable. For this reason, forexample, it is preferable to incorporate an acoustic optical modulatorin the laser beam generator 60.

As shown in FIG. 15, the acoustic optical modulator includes atransparent dielectric 102 sandwiched between a pair of electrodes 104,and is driven by an AOM driver circuit 106 which is operated undercontrol of the system control unit 76 (FIG. 3). The acoustic opticalmodulator is inserted into an optical path through which the laser beampasses. While the acoustic optical modulator is not driven, the laserbeam merely passes through the transparent dielectric 102. When theacoustic optical modulator is driven, the laser beam is subjected todiffraction so as to be deflected from the optical path.

In short, by incorporating the acoustic optical modulator in the laserbeam generator 60, it is possible to maintain the power of laser beamconstant.

Of course, when the acoustic optical modulator is used, it is driven insteps 1108, 1119, 1128 and 1132 of the first laser beam irradiationroutine of FIGS. 11A and 11B and steps 1208, 1219, 1228 and 1232 of thesecond laser beam irradiation routine of FIGS. 12A and 12B, and thedrive of the acoustic optical modulator is stopped in steps 1116, 1126,1130 and 1134 of the first laser beam irradiation routine of FIGS. 11Aand 11B and steps 1216, 1226, 1230 and 1234 of the second laser beamirradiation routine of FIGS. 12A and 12B. Note, a galvano-mirror may besubstituted for the acoustic optical modulator.

Optionally, the optical focusing system 70 (FIG. 2) may include amovable lens which is mechanically moved between a focus position and adefocus position by a suitable actuator. In particular, the movable lensis usually placed at the focus position so that the laser beam isfocused on the silicon wafer. When the movable lens is moved from thefocus position to the defocus position, the laser beam is defocused sothat the material of the multi-layered wiring structure cannot beremoved.

In the above-mentioned embodiment, although each of the alignment marksAM is placed at the cross point of the scribe lines, it may bepositioned at another location. For example, as shown in FIG. 16, analignment mark AM may be placed on the scribe line SSL₁₇ at a locationbetween two adjacent semiconductor chip areas CA. When the alignmentmarks AM is placed at the cross point of the scribe lines, the power ofthe laser beam must be controlled twice to define the alignment markAMA. On the other hand, as shown in FIG. 16, when the alignment mark AMis out of the cross point, it is possible to obtain the alignment markarea AMA by only once controlling the power of the laser beam.

In the above-mentioned embodiment, although the two alignment marks AMare used, it is possible to form more than two alignment marks on thesilicon wafer to improve the positioning precision. Also, when theorientation flat OF of the silicon wafer SW is utilized for positioning,only one alignment mark may be formed on the silicon wafer.

Finally, it will be understood by those skilled in the art that theforegoing description is of preferred embodiments of the methods anddevices, and that various changes and modifications may be made to thepresent invention without departing from the spirit and scope thereof.

1. A semiconductor wafer comprising: a substrate body; a multi-layeredwiring structure formed on said substrate; a scribe line defined on saidmulti-layered wiring structure; and at least one alignment mark formedon said scribe line, said at least one alignment mark being at anuppermost level of said multi-layered wiring structure, wherein saidmulti-layered wiring structure is partially removed from saidsemiconductor wafer along said scribe line, but said alignment mark isleft on said scribe line.
 2. A semiconductor wafer as set forth in claim1, wherein a width of said scribe line is within a range between 40 μmand 70 μm.